They’re connected to a single USB-C cable. For many technical reasons you can’t have a simple kvm which switches inputs. You’ll need to continuously power all 9 minis some way. All nine USB-C cables will need a continuous, active connection.

To do this, you will need a smart controller that switches which port it’s talking to.

Or you can stick a relatively cheap device on every mini and and connect it to the network.

Having a “controller” for every mini means you can swap single units in both hardware and software very easily. There’s a one-to-one relationship and you don’t have to deal with pairing.